Source code in the swift programming language

// See https://en.wikipedia.org/wiki/Divisor_function
func divisorCount(number: Int) -> Int {
    var n = number
    var total = 1
    // Deal with powers of 2 first
    while n % 2 == 0 {
        total += 1
        n /= 2
    }
    // Odd prime factors up to the square root
    var p = 3
    while p * p <= n {
        var count = 1
        while n % p == 0 {
            count += 1
            n /= p
        }
        total *= count
        p += 2
    }
    // If n > 1 then it's prime
    if n > 1 {
        total *= 2
    }
    return total
}

let limit = 32
var n = 1
var next = 1
while next <= limit {
    if next == divisorCount(number: n) {
        print(n, terminator: " ")
        next += 1
        if next > 4 && divisorCount(number: next) == 2 {
            n = 1 << (next - 1) - 1;
        }
    }
    n += 1
}
print()